The fight was ended when Groves dropped Smith with a huge right hook to the side of the head which floored the man from Liverpool.
Smith managed to get to his feet but was still stunned and Groves easily knocked him down again, forcing the referee to stop the fight.
The first round had been quite subdued in comparison, Groves happy to use his jab to keep his opponent at bay and feel his way into the bout.
However, no one predicted that the fight would end in such emphatic circumstances, the victory reaffirming that Groves is both a boxer, as shown in his last fight against James DeGale, and a lethal puncher.
The victory improved Grovesâ€™ perfect record to 14 victories, 11 coming by knockout, while the loss was the third of Smithâ€™s career.
After the fight Groves said: â€œIâ€™m happy with it, the game plan was to control Smith. I used my jab to keep him guessing.
â€œThe knockout came earlier than I thought, I threw the shot and I knew that it was over. You make mistakes and you pay for them.
“Iâ€™m surprised he got up, he was still wobbly on his feet. I saw the opening on the left hand side and I landed right on the button.
“Iâ€™m under stress to improve as a fighter, and you can see what I do when I do. I just want to improve.
When the possibility of a rematch against James DeGale was mentioned Groves added: â€œIâ€™ll leave him [DeGale] in peace, heâ€™s not on my immediate radar. He can sleep easy tonight.â€
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